1. Field of the Invention
The present invention generally relates to a wireless communication system, and in particular, to a signal detection method for a Multiple-Input Multiple-Output (MIMO) communication system employing spatial multiplexing.
2. Description of the Related Art
Generally, a signal transmitted in a wireless environment experiences more distortion than it would if it were transmitted in a wired environment due to various factors such as a multi-path phenomenon, attenuation, time-varying noise, and/or interruption. A fading phenomenon due to the multi-path phenomenon is closely related to reflection caused by a geographical structure and/or movement of a receiver. Accordingly, a transmission signal passing through a fading channel is typically is distorted when it is received which results in a degradation of system performance. As such, the fading phenomenon is a key factor that obstructs high-speed data communication in the wireless environment. Therefore, minimizing a loss in a wireless channel due to factors such as fading and/or user interference is necessary for high-speed data communication in the wireless environment.
To overcome the fading phenomenon, a transmission method using a space diversity scheme can be used. The space diversity scheme includes a transmission antenna diversity scheme using multiple transmission antennas and a reception antenna diversity scheme using multiple reception antennas. A system achieving space diversity using multiple reception antennas and multiple transmission antennas is referred to as a Multiple-Input Multiple-Output (MIMO) system.
In the MIMO system, data that is to be transmitted through a corresponding antenna of multiple transmission antennas is determined by Space-Time Coding (STC). Likewise, when receiving, each of the multiple reception antennas receives a signal transmitted from each of corresponding multiple transmission antennas and performs Space-Time Decoding (STD).
Space-Time Coding (STC) is implemented by a space-time transmission diversity scheme in which the same data is coded into different formats to be transmitted through different transmission antennas or a spatial multiplexing scheme in which different data is transmitted through different transmission antennas.
An STC signal in the spatial multiplexing scheme is generally decoded by a joint or separate detection method at a receiver. The joint detection method should consider not only a signal transmitted from a single transmission antenna but also signals transmitted from other transmission antennas.
For this reason, a maximum likelihood decoding scheme is widely used as the optimal decoding algorithm for an MIMO system employing spatial multiplexing. By using the maximum likelihood decoding scheme, it is possible to acquire a diversity degree that is the same as the number of reception antennas regardless of the number of transmission antennas. Thus, the maximum likelihood decoding scheme exhibits superior performance over other decoding schemes such as a Minimum Mean Square Error (MMSE) scheme and a zero-forcing scheme in terms of a Signal-to-Noise Ratio (SNR) and SNR gain (which increases proportionally to the number of transmission antennas).
However, the complexity of the maximum likelihood decoding scheme increases exponentially as the number of transmission antennas increases, thus, requiring greater computational ability and increasing power usage, cost, and computational time. Accordingly, there is a need for a system and method to reduce computational complexity in a MIMO communication system.